The present invention generally relates to methods and apparatus for crosslinking a silicon carbide fiber precursor polymer. More particularly, the present invention relates to methods and apparatus for efficiently crosslinking a silicon carbide fiber precursor polymer by e-beam radiation.
Silicon carbide (SiC) is one of several advanced ceramic materials which are currently receiving considerable attention as electronic materials, as potential replacements for metals in engines, and for a variety of other applications where high strength, combined with low density and resistance to oxidation, corrosion and thermal degradation at high temperatures is desirable or necessary. Unfortunately, these extremely hard, non-melting ceramics are difficult to process by conventional forming, machining, or spinning applications rendering their use for many of these potential applications problematic. In particular, crosslinking SiC fiber polymer precursors (polycarbosilane and polydisilazane) via e-beam irradiation is the biggest bottleneck in the silicon carbide fiber production process.
Crosslinking SiC fiber polymer precursors (e.g., polycarbosilane and polydisilazane) makes the polymer infusible, so the fiber's dimensional integrity will be maintained during subsequent pyrolysis. Currently, e-beam is the typical mechanism used to effectuate the crosslinking of SiC fiber polymer precursors. However, the throughput of the current crosslinking process is severely limited by temperature increase incurred by the fibers due to the energy absorbed during irradiation. As a result, the radiation dose must be delivered at a rate slow enough to ensure that the SiC fiber polymer precursors do not reach their melting point, and thus lose their shape and/or fuse together.
In typical arrangements the radiation dose is regulated or limited through the use of a conveyor system. After a portion of a preceramic SiC fiber is irradiated, it rides around a long conveyor to cool down in the ambient atmosphere before returning to the e-beam for another small dose of radiation. The portions of the preceramic SiC fiber are passed under the e-beam enough times to receive the cumulative dose needed for effective crosslinking—thereby crosslinking the entire length of the fiber. When large doses (several MGy) are required to effectively crosslink a polymer fiber the radiation process becomes prohibitively expensive due to the large capital investment required in very long conveyor systems and long production times.
Thus, a need exists for methods and apparatus for efficiently crosslinking SiC fiber polymer precursors (e.g., polycarbosilane and polydisilazane) via e-beam while maintaining the fiber's dimensional integrity. Methods and apparatus facilitating e-beam curing of such fibers at much higher rates than prior art methods and apparatus would provide for valuable high throughput, cost-effective commercial silicon carbide fiber production with reduced footprint requirements.